The present invention relates to the art of earth boring and, more particularly, to a bit having land erosion protection on the cutter. During the drilling of boreholes with an insert type bit, the body of the cutter operates in a highly abrasive environment. This abrasive condition exists during drilling operations wherein a drilling mud is utilized as the medium for cooling the bit and carrying the cuttings from the borehole and during drilling operations wherein an air or gas is used as the circulating, cooling and flushing medium.
Bit life and efficiency are of prime importance in the drilling of oil and gas wells, blast holes, raise holes or other types of boreholes, since the penetration rate is more or less directly related to the condition of the bit. When harder formations are encountered during the drilling of the borehole, a bit having carbide inserts projecting from the body of the cutter is generally utilized because of the ability of the inserts to penetrate the hard formations of the earth. However, the carbide inserts are mounted in a relatively soft metal forming the body of the cutter membrane. When such bits are exposed to the abrasive conditions in the borehole, the relatively soft material of the cutter member body which holds the inserts in place is abraded or eroded away. This is primarily due to the presence of relatively fine cuttings from the formation and/or the direct blasting effect of the fluid utilized in the drilling process. The wearing away of the cutter member body is usually most pronounced along the gage row of the cutter members. When the material supporting the inserts is eroded or abraded away to a sufficient extent, the drilling force exerted on the insert, when they engage the formation, either breaks the inserts or forces them out of the cutter member altogether, with the result that the bit is no longer effective in cutting the formation.
When drilling in certain abrasive type formations where the bit is penetrating at a rapid rate, it can be expected that the abrasive formation will be contacting the cone shell on the areas between the inserts due to the depth of penetration of the individual cutting inserts. When this cone shell contact occurs, the softer cone shell material will erode away around the harder insert materials until the insert becomes exposed and the retention in the cone shell is weakened, thus resulting in the loss of the insert and reduction of bit life. The inserts utilized in this type of bit are retained in the cutter member by "hoop" tension generated when the insert is pressed into the relatively soft cutter member body. Accordingly, any method utilized in attempting to alleviate the erosion of the cutter member must take into consideration that the "hoop" tension holding the insert must be retained.